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Introduction

The Test Case Gotein is located on the Saison in the southwest of France. The Saison has a total length of 54 km long and flows along the Pyrenees. Itis a tributary to Gave D’Oloron, which flows into the Adour river.

There are 3 hydropower plants (HPPs) and one fish farm on the Saison.

The hydrology of the Saison is characterized by sustained flows in winter, high water levels in spring due to snow melting and a low water period from August to October. At Gotein the mean interannual discharge is estimated at 22.3 m3/s.

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Gotein hydropower plant

The HPP of Gotein is a run of river HPP with an installed capacity of 0.32 MW. It has a bypassed reach of 2.26 km. The turbine on site is a Kaplan turbine with a maximum turbined flow of 6.6 m3/s and a rated head of 5.81 m.

Characteristics
CountryFrance
RiverSaison
OperatorSociété Hydroélectrique de Gotein
Capacity0.32 MW
Head5.81 m
Inter-annual discharge22.3 m³/s
1 Kaplan turbine

Pressures on the water body's ecosystem
The hydrology of the Saison is highly altered by the hydropower plant of Sainte-Engrâce located more than 25 km upstream, which runs with hydropeaking. The continuity is altered by several weirs and HPPs along its course.

Pressures
Continuitymoderate
Hydrologyhigh
Morphologyminimal

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Test Case topics

Fish population
The river is dominated by cyprinids and salmonids.

Downstream migration
An inclined bar rack (inclination 26°, bar spacing 20 mm) ist located infront of the HPP to protect the fish on their downstream migration. 5.4% of the turbine flow is allocated for downstream migration.

Fish migration
Species: Salmon, see trout, lamprey, eel, brown trout
baffle fishway and eelpass for upstream migration
Inclined bar rack for downstream migration

Upstream migration
At the dam, the fishes can use a pre-barrage fish pass to go upstream (2014). A flow of 1 m3/s is maintained in the pass. The pass has two pools of 38 and 45 m². It targets the fishes using the bypassed reach to go upstream.

At the powerplant, the fishes can use a baffle fishpass composed of 5 portions of 7.5 m with a 16% slope. The portions are connected by pools (3.0x2.0x1.0m). The flow in the fishpass is 150 l/s. There is a specific device for eels: it is composed of 4 portions, each 4 to 6 m long, with a 25 to 30 % slope. These are connected by resting pools (1.5x1.0x0.5m). The flow allocated to the fish pass is only a few liters per second. These devices target the fish using the tailrace channel to go upstream.

E-flow
In France, the law of 2006 (LEMA) imposes an e-flow of 1/10 of the mean inter-annual discharge before 1rst January 2014. They are two options for the environmental flow in the bypass section.

The first one is a minimum value equal to a tenth of the mean interannual discharge of the water course. It’s the value chosen in Gotein 2.5 m3/s.

The second one is a minimum biological flow value. It is calculated thanks to deep habitat studies. In the case of the value founded with the study is greater than the minimum value, it becomes the new minimum flow. If it’s smaller, the minimum flow stays equal to the tenth of the mean interannual discharge.

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Research objectives and tasks

The test case site of Gotein is a small HPP with a fishfriendly water intake. For FIThydro, the efficiency of this water intake will be assessed. To assess the influence of the bypass and undertake modifications of the flow conditions, hydraulic modelling will be done for the entrance of the HPP.

Research tasks
The research task and field studies conducted at Gotein are:

  • Radiotelemetry fish tracking (Atlantic salmon smolts and silver eels) for the assessment of the bar rack efficiency
Research objectives
Fish migration
Water intake

Main FIThydro partners involved in the research at Gotein

Research topicsFIThydro partners
HydropeakingCNRS

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pictures: © Pôle Ecohydraulique de l'AFB